Mod_jk is connector that communicates with apache web server and tomcat. We need to download and copy that connector in module folder of apachehttp://tomcat.apache.org/connectors-doc/ we are using latest connector of mod_jk
Make mod_jk.log file in logs folder otherwise apache will throw error
RENAME MOD_JK.SO OR MOD_JK.[WINDOWS]

Make a file with name of workers.properties in conf folder. This file tells properties of all tomcat instances. We have to specify all tomcat properties here. Apache will forword request to tomcat through this file
Vertical tomcat clustering this file like

Check clustering if apache start properly, It is fine without any errors otherwise check problems,basically mod_jk problems come. So download different mod_jk for your machine. Start all tomcats, tomcatA, tomcatB, and tomcatC. If all tomcats is started this means tomcat is working fine.
Open test.jsp on browser and check session id. Check which tomcat on test.jsp is running tomcatB or tomcatC. Close that tomcat, reload test.jsp. Check session id,if session id is same. Then tomcat clustering is working fine.

If the Tomcat Host appBase (webapps) directory is accessible by the Apache web server, Apache can be configured to serve web application context directory static files instead of passing the request to Tomcat.
Caution: For security reasons is is strongly recommended that JkMount is used to pass all requests to Tomcat by default and JkUnMount is used to explicitly exclude static content to be served by httpd. It should also be noted that content served by httpd will bypass any security constraints defined in the application's web.xml.
Use Apache's Alias directive to map a single web application context directory into Apache's document space for a VirtualHost: